Subject: Re: time series in R
From: Adrian Trapletti (Adrian.Trapletti@wu-wien.ac.at)
Date: Tue 20 Jul 1999 - 18:50:18 EST
Prof Brian D Ripley wrote:
> If Martyn and Adrian are agreeable, I will start a library(ts) in the
> 0.65 version. I will put in this:
I agree with almost everything.
> the ts class and methods (maybe in due course these should be removed
> from the base package?)
> datasets from MASS, tseries
> lag, deltat, cycle
> acf from bats, augmented by ideas from tseries.
> spectrum, spec.pgram from bats (after looking at tseries hard)
Concerning the normalization, definition of fft and so on, I just want to say how
it is done in tseries:
Periodogram: Normalizing by (2*pi*n) where n is the length of the original series,
i.e. it differs from Brockwell&Davies by the factor 2*pi. Furthermore, normalizing
by n (and not npad) preserves the shape and not the sum under/over the
periodogram. I also remove the mean before starting the main computation which
makes the correction (10.4.7) from B&D unnecessary(?).
> cpgram from MASS
> ar.yw from bats (although that probably needs to be moved to
> C/Fortran, and I may special-case the univariate case to use code I
> have for that).
What about simple OLS estimator ar.ols?
> That leaves
> stl -- I believe the code for this is on netlib.
> arima modelling. I do have Fortran code for this, and will work on
> a simple R interface for it. An elegant interface can come later.
> As the feature-freeze for 0.65 is probably about 2-3 weeks away, we
> ought to concentrate on getting the basic stuff (bats-like) in first.
I will wait until this first version is finished and then update the tseries
library to fit with the R ts.base library so we can use, e.g., the tests etc. What
about the name tseries. Should I change this name, so that it does not conflict
with the time series base?
-- Adrian Trapletti, Vienna University of Economics and Business Administration, Augasse 2-6, A-1090 Vienna, Austria Phone: ++43 1 31336 4561, Fax: ++43 1 31336 708, Email: firstname.lastname@example.org
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